#!/bin/bash# SPDX-License-Identifier: GPL-2.0## Here's how to use this:## This script is used to help find functions that are being traced by function# tracer or function graph tracing that causes the machine to reboot, hang, or# crash. Here's the steps to take.## First, determine if function tracing is working with a single function:##   (note, if this is a problem with function_graph tracing, then simply#    replace "function" with "function_graph" in the following steps).##  # cd /sys/kernel/tracing#  # echo schedule > set_ftrace_filter#  # echo function > current_tracer## If this works, then we know that something is being traced that shouldn't be.##  # echo nop > current_tracer## Starting with v5.1 this can be done with numbers, making it much faster:## The old (slow) way, for kernels before v5.1.## [old-way] # cat available_filter_functions > ~/full-file## [old-way] *** Note ***  this process will take several minutes to update the# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we# [old-way] are dealing with thousands of functions. So go have coffee, talk# [old-way] with your coworkers, read facebook. And eventually, this operation# [old-way] will end.## The new way (using numbers) is an O(n) operation, and usually takes less than a second.## seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file## This will create a sequence of numbers that match the functions in# available_filter_functions, and when echoing in a number into the# set_ftrace_filter file, it will enable the corresponding function in# O(1) time. Making enabling all functions O(n) where n is the number of# functions to enable.## For either the new or old way, the rest of the operations remain the same.##  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file#  # cat ~/test-file > set_ftrace_filter##  # echo function > current_tracer## If it crashes, we know that ~/test-file has a bad function.##   Reboot back to test kernel.##     # cd /sys/kernel/tracing#     # mv ~/test-file ~/full-file## If it didn't crash.##     # echo nop > current_tracer#     # mv ~/non-test-file ~/full-file## Get rid of the other test file from previous run (or save them off somewhere).#  # rm -f ~/test-file ~/non-test-file## And start again:##  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file## The good thing is, because this cuts the number of functions in ~/test-file# by half, the cat of it into set_ftrace_filter takes half as long each# iteration, so don't talk so much at the water cooler the second time.## Eventually, if you did this correctly, you will get down to the problem# function, and all we need to do is to notrace it.## The way to figure out if the problem function is bad, just do:##  # echo <problem-function> > set_ftrace_notrace#  # echo > set_ftrace_filter#  # echo function > current_tracer## And if it doesn't crash, we are done.## If it does crash, do this again (there's more than one problem function)# but you need to echo the problem function(s) into set_ftrace_notrace before# enabling function tracing in the above steps. Or if you can compile the# kernel, annotate the problem functions with "notrace" and start again.#  if [ $# -ne 3 ]; then  echo 'usage: ftrace-bisect full-file test-file  non-test-file'  exitfi full=$1test=$2nontest=$3 x=`cat $full | wc -l`if [ $x -eq 1 ]; then	echo "There's only one function left, must be the bad one"	cat $full	exit 0fi let x=$x/2let y=$x+1 if [ ! -f $full ]; then	echo "$full does not exist"	exit 1fi if [ -f $test ]; then	echo -n "$test exists, delete it? [y/N]"	read a	if [ "$a" != "y" -a "$a" != "Y" ]; then		exit 1	fifi if [ -f $nontest ]; then	echo -n "$nontest exists, delete it? [y/N]"	read a	if [ "$a" != "y" -a "$a" != "Y" ]; then		exit 1	fifi sed -ne "1,${x}p" $full > $testsed -ne "$y,\$p" $full > $nontest